1. Field of the Invention
This invention relates to an electromagnetic-wave absorber comprising a base material and fixed thereon particles having electric-wave or electromagnetic-wave absorptivity, and a process for its production. More particularly, this invention relates to an electromagnetic-wave absorber having superior workability and superior handling properties in the shape of paper, and a process for its production.
2. Related Background Art
As electromagnetic-wave absorbers for microwaves and millimeter waves, conventionally used are composite materials of polymers or foamed polymers with magnetic materials such as ferrite particles. Also used are composite materials of polymers with silicon carbide fibers. They, however, have not achieved any sufficient electromagnetic-wave absorptivity over a wide frequency range. An absorber is also devised which is formed of a composite of a polymer with carbon fibers to one side of which an electrically conductive material of aluminum or the like has been stuck. This absorber, however, has had problems that it involves a directionality in its absorptivity and can be made to have a complicated form with difficulty. A composite material of a rubber with a ferrite material has also been put into practical use, which, however, is too heavy to be applicable to constructions with ease. These electromagnetic-wave absorbers are composites of polymers or rubbers with particles or fibers having electromagnetic-wave absorptivity which have been made into composites by some methods, and have had a problem that they require complicated production processes.
A method is also used in which particles having electromagnetic-wave absorptivity are mixed with a coating material or an adhesive and the mixture formed is coated on or applied to necessary portions. According to this method, however, it is difficult to finish its coating or application in uniform characteristics over a wide area of, e.g., room or building walls, and also there is a disadvantage that the coated or applied material tends to come off during use. In addition, a problem is involved such that the quality and the coming-off after coating or application can be managed with difficulty. Also, there is another problem that the mixture is used like a coating material and hence can be recycled with difficulty.
An object of the present invention is to eliminate the above disadvantages and provide an electromagnetic-wave absorber which can readily be used at portions where electromagnetic-waves must be absorbed, and has an electromagnetic-wave absorption layer on a thin base material which can be recycled with ease.
Another object of the present invention is to provide a process for producing a novel electromagnetic-wave absorber by which an electromagnetic-wave absorption layer can readily be formed on a thin base material which can readily be worked and handled.
The present inventors have made extensive studies on electromagnetic-wave absorbers which can readily be worked and have superior electromagnetic-wave absorptivity. As the result, they have discovered that an electromagnetic-wave absorber having a thin base material provided thereon with an electromagnetic-wave absorption layer containing at least i) a polymeric material having a specific Tg (glass transition temperature) and an Mn (number-average molecular weight) and ii) an inorganic material has superior electromagnetic-wave absorptivity. Thus, they have accomplished the present invention. They also have discovered that such an electromagnetic-wave absorber having superior electromagnetic-wave absorptivity can readily be produced by causing electromagnetic-wave absorption particles to adhere to a thin base material by the aid of static electricity; the particles containing at least a polymeric material and an inorganic material; and heating the particles. Thus, they have accomplished the present invention.
More specifically, the present invention provides an electromagnetic-wave absorber comprising a base material and an electromagnetic-wave absorption layer provided on the base material, wherein;
the electromagnetic-wave absorption layer contains at least i) a polymeric material having a glass transition temperature (Tg) of from xe2x88x9215xc2x0 C. to 110xc2x0 C. and a number-average molecular weight (Mn) of from 3,000 to 1,000,000 and ii) an inorganic material.
The present invention also provides an electromagnetic-wave absorber comprising a base material and an electromagnetic-wave absorption layer provided on the base material, wherein;
the electromagnetic-wave absorption layer is a layer formed by:
causing electromagnetic-wave absorption particles to adhere to the base material by the aid of static electricity; the particles containing at least a polymeric material and an inorganic material; and
heating the electromagnetic-wave absorption. particles to fix them to the base material.
The present invention further provides a process for producing an electromagnetic-wave absorber comprising:
an adhesion step of causing electromagnetic-wave absorption particles to adhere to a base material by the aid of static electricity; the particles containing at least a polymeric material and an inorganic material; and
a fixing step of fixing the electromagnetic-wave absorption particles to the base material by heating, to form an electromagnetic-wave absorption layer.
According to the present invention, an electromagnetic-wave absorber having the shape of thin paper can readily be obtained and also it can be made to have any shape of paper or cloth. Moreover, in the production of the electromagnetic-wave absorber, copying machines and printers utilizing electrophotographic processes can be used, and hence absorbers having a high function can be obtained at a very low cost. As the result, their use on walls or the like of buildings promotes effective utilization of electromagnetic waves in electronic machinery and highly information-oriented society, and this is effective also for removing any obstacles to human bodies caused by electromagnetic waves.